A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces. When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read-write head that is positioned over a specific location of a disk by an actuator. A read-write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. A write head makes use of the electricity flowing through a coil, which produces a magnetic field. Electrical pulses are sent to the write head, with different patterns of positive and negative currents. The current in the coil of the write head induces a magnetic field across the gap between the head and the magnetic disk, which in turn magnetizes a small area on the recording medium.
High volume magnetic thin film head slider fabrication involves high precision subtractive machining performed in discrete material removal steps. Slider processing starts with a completed thin film head wafer consisting of 40,000 or more devices, and is completed when all the devices are individuated and meet numerous and stringent specifications. Each individual device ultimately becomes a read-write head (e.g., Perpendicular Magnetic Recording (PMR) heads) for flying over a spinning disk.
Increasing areal density (a measure of the quantity of information bits that can be stored on a given area of disk surface) is one of the ever-present goals of hard disk drive design evolution, and has led to the necessary development and implementation of various means for reducing the disk area needed to record a bit of information. Precise control of the critical dimensions of a read head element and a write head element, by way of machining and lapping, are commonly practiced and are a necessity of manufacturing. Of continued importance is the alignment of the read and write portions of the head relative to each other. For optimum yield, performance and stability, precise dimensional control over both the reader and/or writer elements is desirable.
For example, process improvements regarding the magnetic core width (MCW) (as well as the magnetic erase width (MEW), magnetic write width (MWW), magnetic interference width (MIW), and other related magnetic core measures) would benefit areal density because the MCW effectively determines the width of a magnetic bit recorded by the write head. Furthermore, the single largest contributor to the overall MCW sigma is typically the “within row-bar” sigma. Even though manufacturing processes are developed to produce read-write heads having MCW as close as possible to a desired MCW for the system, some thin-film and other manufacturing processes (e.g., lithography, etching, rough lapping, material elasticity, etc.) experience inherent variations that make it quite challenging to achieve the desired MCW for every read-write head manufactured.
Any approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.